Honestly, this was just a one-off project, which turned out quite fine.
Shader itself is has picture resampling with downscaling, and most importantly – it has aspect ratio correction.
So to example, 256×224 at 4:3 will actually result in 434×224 at 16:9.
On top of that – it uses Bayer dithering and paletting, (with adjustable bleed (exposure if you like), and brightness), making it a good choice if you need to give your project a retro flair.
Just be aware that you must do some work yourself – i recommend making your scenes contrast-rich, and adding more character to the lighting (rather than keeping it plain).
You can buy it here https://www.assetstore.unity3d.com/en/#!/content/57038